Most barcode or receipt printers have an index sensor feature for allowing the printer to register the print on each printed label or receipt. The index sensor utilizes a periodic, pre-printed, black band disposed on the back side of a roll of supply media, which is dispensed as a moving web continuum. Periodic holes cut into the media, or the gaps between the labels, can also be used as a registration means.
A typical index sensing apparatus consists of a light emitting diode (LED) and a light detector. The index sensing apparatus is disposed opposite the back side surface the moving media web. The LED directs light at the back side of the media, which reflects the light back to the light detector. As a black band moves past the LED, the emitted light from the LED fails to be reflected from the black band. It is this absence of light that is sensed by the detector. Every time a black band is sensed, the index sensing apparatus provides a registration signal. Holes in the media web have the same effect as black bands, since light passes through the holes and fails to be reflected.
Most printers have fixed index sensing positions, from side to side, within the media cavity. One of the problems associated with these index sensing apparatuses are their lack of uniformity of mounting. The precise position of the LED and the light detector, in a given relationship with respect to the media, often has to change. Changing the media size or the media brand necessitates a repositioning of the index sensing apparatus. This is not possible with printers that have a fixed index sensing position.
The present invention seeks to provide a universal index sensing apparatus that can easily be adjusted for different brands of media and changes in the media size. The universal index sensing apparatus can be molded to fit mounting configuration within the media cavities of different printers.